Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$179.74	6.338%	$191.1319	$191.13	$191.15	$191.10
Purchase #2	$32.72	3.531%	$33.8753	$33.88	$33.90	$33.90
Purchase #3	$133.68	4.494%	$139.6876	$139.69	$139.70	$139.70
Purchase #4	$220.98	5.762%	$233.7129	$233.71	$233.70	$233.70
Purchase #5	$158.98	12.821%	$179.3628	$179.36	$179.35	$179.40
Purchase #6	$66.48	3.630%	$68.8932	$68.89	$68.90	$68.90
Purchase #7	$48.25	10.183%	$53.1633	$53.16	$53.15	$53.20
7 purchase totals =	$840.83		$899.8270	$899.82	$899.85	$899.90